The preferred embodiment concerns a method and a device to fix print images on a recording material.
For single-color or multicolor printing of a recording material, for example of a single page or of a belt-shaped recording material made of the most varied materials (for example plastic, paper or thin metal films), it is generally known: to generate image-dependent potential images (charge images) on a potential image carrier, for example a photoconductor; to ink these in a developer station (inking station); and to transfer-print the image developed in such a manner on the recording material. To develop the potential images it is known to apply printing fluid to the recording material in an electrophoretic method. It is also known to transfer-print images onto a recording material via rollers and a printing plate in an offset printing method.
The printing fluid is a liquid developer in digital printing or oil-based ink in offset printing. For example, the printing ink has silicone oil, mineral oil and/or a liquid that can be photo-polymerized (the fluid being designated as carrier fluid) and toner particles, color pigments and/or dyes which are chromophoric solid particles. Moreover, additional substances can be added to the carrier fluid, for example fountain solution, charge control substances, initiators and/or agents affecting the surface tension or viscosity.
The print images are transfer-printed onto the recording material with the chromophoric solid particles. In contrast to this, the carrier fluid is required to (among other things) transfer the solid particles to the potential image carrier, the rollers, the print plate or the recording material and can be distributed over the entire width of the recording material, independent of the print images. In the fixing of the applied image, the carrier fluid applied to the recording material is vaporized in a drying chamber connected to a printer. The chromophoric solid particles applied to the recording material are fused upon fixing the print images after the vaporization of the carrier fluid and thereby bond with the recording material. Other printing fluids are also known in which, upon heating, the carrier fluid polymerizes in a cross-linking manner such that it fixes the chromophoric solid particles in their position, wherein solid particles can thereby be used that do not fuse upon being heated. In offset printing the oil-based ink (comprised of carrier fluid and dye pigments) is initially transfer-printed onto the recording material and partially penetrates into the pores of the recording material. The carrier fluid is subsequently vaporized.
For example, the fusing of the chromophoric solid particles, the vaporization of the carrier fluid or the polymerization of the carrier fluid takes place with the aid of infrared radiation, flash fixing, heat-pressure rollers, or hot air. An air/oil mixture forms in the drying chamber due to the vaporized carrier fluid, in particular vaporized oil. In the fixing of the print images the recording material is heated to temperatures between 90 and 160 degrees Celsius and the air/oil mixture is heated to temperatures up to 300 degrees Celsius. With increasing operation duration of the drying chamber, the concentration of the vaporized carrier fluid (and therefore the oil ratio in the air/oil mixture) also increases. The concentration of the vaporized carrier fluid in the air/oil mixture can thus be so high that an acute explosion risk exists. The lower limit of the concentration as of which an acute explosion risk exists is also called the lower explosion limit (LEL). The air/oil mixture is regularly thinned with fresh air so that the LEL is not exceeded. A further variable that has an effect on the explosion risk is the temperature of the air/oil mixture. A cooling of the air/oil mixture is avoided in that the fresh air is preheated, for example with a hot air dryer. The air/oil mixture must be recycled (which is expensive and complicated) in that the oil portion is removed from the air/oil mixture.